Internal combustion engines such as, for example, diesel engines, gasoline engines, and gaseous fuel powered engines, combust a mixture of air and fuel to produce power. The amount of air and fuel, and the ratio of air-to-fuel introduced into a combustion chamber of the engine can affect power output, efficiency, and exhaust emissions of the engine. Typically, the amount of air introduced into the engine and the ratio of air-to-fuel are controlled by a number of different fluid handling components located in both the air induction and exhaust systems of the engine.
An engine often includes a turbocharger to increase a power density of the engine. A turbocharger includes a turbine, driven by exhaust of the engine, to rotate a compressor and pressurize air directed into the engine. As more exhaust is directed to the turbine, the turbine rotational speed increases, thereby causing the compressor rotational speed to increase, which raises the pressure of air being directed into the engine. However, if the speed of turbine rotation is above an overspeed limit, damage may occur to the components of the turbocharger.
One method that has been employed to prevent the speed of the turbocharger from exceeding the overspeed limit can be found in U.S. Pat. No. 6,725,659 (the '659 patent) issued to Shao et al. on Apr. 27, 2004. The '659 patent discloses a fueling control system that generates a fueling signal for an engine based on various fuel limits stored in a memory of the control system. Among the fuel limits included in the fueling control system is an air-to-fuel or oxygen-to-fuel control (AFC/OFC) table, which controls fueling based on an air-to-fuel ratio. Another fueling limit included in the fueling control system is a turbo speed limit for limiting the rotational speed of the turbocharger. Both the AFC/OFC limit and the turbo speed limit are set and activated in response to various parameters of the engine system. When the final fueling signal is generated by the fueling control system, the limits stored within the memory are compared to each other. The limit having the lowest value is used as an upper threshold for the fueling rate.
Although the system disclosed in the '659 patent may set an upper limit for the turbocharger speed, the efficiency of the turbocharger and any protection from overspeed damage may be limited. In particular, the '659 system relies on engine parameters such as, for example, boost pressure, engine acceleration, etc. to set the turbo speed limit and determine when to invoke such a limit. Such parameters may indicate an estimated turbocharger speed but do not measure the actual turbocharger speed. Any error between the estimated speed and the actual speed may have consequences regarding the performance of the turbocharger. For example, if the actual speed is less than the estimated speed, the turbine may not be permitted to reach its full power generation capacity, thereby reducing efficiency. In addition, if the actual speed is greater than the estimated speed, the turbocharger speed may exceed the overspeed threshold and possibly damage the turbocharger.
The disclosed system is directed to overcoming one or more of the problems set forth above.